Stress corrosion cracking in welded steel articles and particularly intergranular stress corrosion cracking in welded austenitic stainless steel piping is apparently attributable to the interactive presence of a corrosive environment, sensitization of the steel by welding heat, alloying element content and other metallurgical factors, and by the presence of residual tensile stresses adjacent to a weld area.
Intergranular stress corrosion cracking in steel and particularly in the vicinity of welded joints in austenitic stainless steel piping employed in nuclear power plant water lines has long been recognized as a serious problem in the art. Diverse solutions to this long standing problem have been proposed, such as the early suggestions of solution annealing, the application of overlay weld bridging extending beyond the original weld concurrent with flow of coolant fluid within the pipe as taught in the Hanneman et al U.S. Pat. No. 4,049,186 and the rapid heating of localized sensitized areas by the generation of a high frequency alternating current within the pipe by induction, or by internal [I.sup.2 R] resistance heating followed by a rapid liquid quenching as suggested by the Eguchi et al U.S. Pat. No. 4,168,190. More recent suggestions, advanced in light of knowledge that one significant probable cause of intergranular stress corrosion cracking in the vicinity of welded joints in nuclear power plant austenitic stainless steel piping was the existance of residual tensile stresses adjacent the joint location, have been to induction heat the pipe by the passage of current therethough intermediate a pair of electrode elements disposed in spaced relation on the outer pipe surface while coolant fluid flows through the pipe as suggested by Matsuda et al U.S. Pat. No. 4,229,235. Matsuda also pointed out that by the application of such heat, the normally existing residual tensile stress on the interior wall of the pipe could be reduced and possibly converted into a residual compressive stress with an accompanying reduction of "corrosion fatigue". More recent suggestions include the selective shaping of induction heating elements or coils to try to control the temperature distribution over the area of application as suggested by Terasaki U.S. Pat. No. 4,354,883 and Sugihura et al U.S. Pat. No. 4,505,763. Neither the use of welded overlays or the use of current flow through the pipe intermediate a pair of applied electrodes has proved to be particularly efficacious, due, at least in part, to the inherent inability to control the temperature gradients within the metal and to the localized environmental difficulties presented by in situ welding. Induction heating of the pipe, while theoretically attractive, requires as a practical matter expensive and bulky equipment such as special high frequency power supplies, impedance matching equipment, cooling media for the induction coils and power cables, and related pumping equipment as well as carefully positioned shielding, all constituting practical problems exacerbated by the complex geometry of installations at valves, tees, elbows, crossovers and the like, that require specially designed induction coil and shielding components.